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Cambridge International Examinations

Cambridge International Advanced Subsidiary and Advanced Level

*2605952040*CHEMISTRY

9701/52

May/June 20171 hour 15 minutes

Paper 5 Planning, Analysis and Evaluation

Candidates answer on the Question Paper.No Additional Materials are required.READ THESE INSTRUCTIONS FIRST

Write your Centre number, candidate number and name on all the work you hand in.Write in dark blue or black pen.

You may use an HB pencil for any diagrams or graphs.Do not use staples, paper clips, glue or correction fluid.DO NOT WRITE IN ANY BARCODES.

Answer all questions.

Electronic calculators may be used.

You may lose marks if you do not show your working or if you do not use appropriate units.Use of a Data Booklet is unnecessary.

At the end of the examination, fasten all your work securely together.

The number of marks is given in brackets [ ] at the end of each question or part question.

This document consists of 13 printed pages and 3 blank pages.

IB17 06_9701_52/4RP© UCLES 2017

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In 1804 the chemist John Dalton put forward the following idea. It is sometimes called ‘Dalton’s Law’.

‘When two elements combine with each other to form more than one compound, the ratios of the masses of one element that combine with a fixed mass of the other element are simple whole numbers.’

A student used the apparatus shown to find out if Dalton’s Law is true for three oxides of lead. Methane gas reduced the heated lead oxides to lead.

excess methaneburning

porcelain boatcontaininglead oxide Amethanegas

heatporcelain boatcontaininglead oxide Bporcelain boatcontaininglead oxide Cheatheat

Lead and oxides of lead are harmful by inhalation and if swallowed. They are very toxic to aquatic organisms and may cause long-term damage in the aquatic environment.(a)State two hazards associated with experimenting with lead oxides.

F or each hazard, state a precaution (other than eye protection) that the student could take to make sure that the experiment is carried out safely.

hazard 1 .....................................................................................................................................

precaution ..................................................................................................................................

....................................................................................................................................................hazard 2 .....................................................................................................................................

precaution ..................................................................................................................................

....................................................................................................................................................

[2]

The student used the following procedure for the experiment.● ● ● ● ● ●

Three clean, dry porcelain boats were weighed when empty. Each boat was filled with a different lead oxide, labelled A, B or C and reweighed. The boats were placed in the apparatus and methane gas passed through. All three samples were heated strongly until they were reduced to lead. The boats were allowed to cool completely with the methane gas still passing over them before they were re-weighed. The results are shown in the table.

mass of

porcelain boat / g5.265.125.23

mass of mass of boat boat + lead + lead after oxide / gheating / g

9.318.9610.52

9.048.4810.06

mass of lead that

was combinedwith 1.0 g oxygenin the lead oxide / g

lead oxide

mass of lead / gmass of oxygen / g

ABC

(b) Complete the table. Record the mass of lead that was combined with 1.0 g of oxygen in the

lead oxide to one decimal place.U se the space below for any necessary calculations.

[2]

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calculate the ratio of mass of lead in each compound.

mass of lead in A : mass of lead in B : mass of lead in C

............................ : ............................ : ............................

[1]

(ii) If Dalton’s Law is true there should be a simple whole number ratio of the masses of

lead in each compound combined with a fixed mass of oxygen.

se your answer to (i) to state and explain whether the student’s experimental results U

support Dalton’s Law.

(d) In this experiment, identify

t he independent variable,

....................................................................................................................................................t he dependent variable.

.................................................................................................................................................... [2]

(e) (i) A nother sample of lead oxide B was found to contain 3.067 g lead and 0.474 g oxygen.

alculate the empirical formula of B. Show your working.C

[Ar: Pb, 207.2; O, 16.0]

empirical formula of B = .............................. [1]

9701/52/M/J/17

(ii) What additional piece of information is required to calculate the molecular formula of B?

....................................................................................................................................... [1]

(f) Before the porcelain boats containing the lead were weighed, they were allowed to cool completely with the methane gas still passing over them.

A part from the hazards associated with handling hot apparatus, explain why this procedure is essential to ensure that the results are reliable.

W hat should the student do to make sure all the lead oxide C had been reduced?

[Total: 12]

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2 When light passes through solutions of chemical compounds some of the light may be absorbed. The quantity of light absorbed is called the absorbance and it is measured by a spectrophotometer. A simplified diagram of a spectrophotometer is shown. A glass cuvette is a rectangular vessel.

sample of solutionlight detectorlight of onewavelength

glass cuvette(a) (i) A chemist placed distilled water in the glass cuvette. This was then put into the

spectrophotometer and a reading taken.

Explain why this reading was taken.

Explain why this procedure makes the readings more accurate.

Manganese is added to steel to increase its strength. A spectrophotometer can be used to analyse the manganese content of steel. This is done by comparing the absorbance of a solution of

–

MnO4(aq) prepared from a sample of steel, with the absorbance of solutions of known concentrations of MnO4–(aq).

(b)1.0 dm3 of a standard solution of 0.0300 mol dm–3 MnO4– was prepared by a chemist using solid

potassium manganate(VII), KMnO4, measured using a two decimal place balance.

(i) C alculate the mass of KMnO4 required to prepare this standard solution.

[Ar: K, 39.1; Mn, 54.9; O, 16.0]

mass of KMnO4 = .............................. g [1]

(ii) Describe how the chemist should accurately prepare this standard solution using a sample

of KMnO4 of mass calculated in (i). There is a 1.0 dm3 volumetric flask available.

........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................ [2](iii) The chemist diluted this standard solution to 3.0 × 10–4 mol dm–3 for use in the experiments.

xplain why the chemist did not prepare a solution of this concentration directly, by E

dissolving the required mass of KMnO4 in 1.0 dm3 of water.

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of MnO4–(aq). The clean, dry cuvette was filled with 3.0 × 10–4 mol dm–3 MnO4– and different wavelengths of light were passed through the solution. A graph of the results was plotted.0.7600.7500.7400.7300.7200.7100.700absorbance0.6900.6800.6700.6600.6500.6400.6300.6200.6100.600

510

515520525530wavelength / nm

535540545550

U se the graph to estimate the wavelength of light that is most absorbed by the MnO4– solution.

wavelength of light most absorbed = .............................. nm [1]

Question 2 continues on the next page.

9701/52/M/J/17

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(d) The spectrophotometer was then set to the wavelength that is most absorbed by the

–

MnO4(aq) solution.

T he chemist measured the absorbance of solutions of known concentrations of MnO4–(aq). The results are shown in the table.

concentration ofMnO4–(aq) / mol dm–3

3.00 × 10–42.70 × 10–42.40 × 10–42.10 × 10–41.80 × 10–41.50 × 10–41.20 × 10–40.90 × 10–40.60 × 10–4

absorbance0.7480.6800.6100.5300.4400.3780.3150.2300.150

(i) P lot a graph on the grid on page 11 to show the relationship between the absorbance and

the concentration of MnO4–(aq).

Use a cross (×) to plot each data point. Draw a line of best fit. [2](ii) State the relationship between absorbance and concentration of MnO4–(aq). Explain your answer with reference to particles.

0.800

0.700

0.600

0.500

absorbance

0.400

0.300

0.200

0.100

0.000

0.00

0.50 × 10–41.00 × 10–41.50 × 10–42.00 × 10–42.50 × 10–43.00 × 10–43.50 × 10–4

concentration of MnO4–(aq) / mol dm–3

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(e) (i) T he chemist used the MnO4–(aq) solution of concentration 3.00 × 10–4 mol dm–3 to prepare

the solutions in the table on page 10.

alculate the volume of 3.00 × 10–4 mol dm–3 MnO4–(aq) solution and the volume of distilled C

water required to prepare a 25.00 cm3 solution of 2.70 × 10–4 mol dm–3 MnO4–(aq).Give your answers to two decimal places.

volume of 3.00 × 10–4 mol dm–3 MnO4–(aq) solution = .............................. cm3

volume of distilled water = .............................. cm3

[1]

(ii) The volumes of the two solutions given in (e)(i) could be measured using the same type of

apparatus.

Name a suitable piece of apparatus which could be used to measure these volumes.

....................................................................................................................................... [1]

The chemist dissolved a known mass of steel, containing manganese, in acid. The manganese was

then oxidised to manganate(VII) ions, MnO4–, using a very strong oxidising agent. The resulting solution was made up to 100.0 cm3 in a volumetric flask.

(f) A small sample of the solution of MnO4–(aq) prepared from the steel sample was placed into a

clean, dry cuvette and its absorbance measured using the spectrophotometer.

(i) The absorbance of the MnO4–(aq) solution was 0.630.

se the graph you have drawn in (d)(i) to determine the concentration of MnO4–(aq) in this U

solution.

Give your answer to three significant figures.

concentration of MnO4–(aq) = .............................. mol dm–3 [1]

(ii) Calculate the mass of manganese present in the steel sample. Show your working.

[Ar: Mn, 54.9]

mass of manganese = .............................. g [1]

9701/52/M/J/17

(g) The steel sample that the chemist used had a mass of 1.209 g.

U se the mass of manganese you calculated in (f)(ii) to calculate the percentage of manganese

by mass that was present in the steel sample.( If you were unable to calculate an answer to (f)(ii) you may use 0.00143 g as the mass of manganese. This is not the correct answer.)

percentage of manganese in the steel sample = .............................. % [1]

(h) Another way of analysing the manganese content of the steel sample is by titration. The steel

sample is prepared in the same way as previously. It is dissolved in acid and then oxidised using a very strong oxidising agent. The MnO4–(aq) ions produced are titrated with a solution of iron(II) ions. The equation for this reaction is shown.

MnO4–(aq) + 8H+(aq) + 5Fe2+(aq) Mn2+(aq) + 5Fe3+(aq) + 4H2O(l)

E xplain why it is essential to remove the strong oxidising agent used to prepare the solution of steel sample before carrying out the titration.

[Total: 18]

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